A spark plug used in a combustion device such as an internal combustion engine includes, for example, a center electrode extending in an axial direction, an insulating body provided on the outer periphery of the center electrode, a cylindrical metal shell mounted on the outer side of the insulating body, and a ground electrode whose proximal end portion is joined to the leading end portion of the metal shell. The ground electrode is disposed with an approximately intermediate portion thereof bent back in such a way that the leading end portion thereof is opposed to the leading end portion of the center electrode, thereby forming a spark discharge gap between the leading end portion of the center electrode and the leading end portion of the ground electrode.
Also, in recent years, a technology has been known whereby a noble metal tip is provided in a region of the leading end portion of the center electrode or ground electrode which forms the spark discharge gap, thus improving wear resistance. A laser welding using a YAG laser is commonly used in joining the noble metal tip and the ground electrode or the like (for example, refer to Patent Japanese Patent Application Laid-Open (kokai) No. 2003-17214). That is, the outer periphery of the boundary portion between the noble metal tip and the ground electrode or the like is intermittently irradiated with a laser beam to form a melt portion wherein their individual components melt together, thereby joining the noble metal tip and the ground electrode or the like.